HIE-ISOLDE LINAC '''REX'''

The aim of the HIE-ISOLDE project is to greatly expand the physics programme compared to that of REX-ISOLDE. HIE-ISOLDE forms part of the European nuclear physics strategy, and its science case covers the majority of the key questions in nuclear structure and astrophysics pursued by our community.

The HIE-ISOLDE project contains three major elements: higher energies, improvements in beam quality and flexibility, and higher beam intensities. This requires developments in radioisotope selection, improvements in charge-breeding and target-ion source development, as well as construction of the new injector for the PS Booster, LINAC4. The most significant improvement will come from replacing most of the existing REX accelerating structure by a superconducting (SC) linear accelerator with a maximum energy of 10 MeV/u. This would allow all ISOLDE beams to be accelerated to energies well below and significantly above the Coulomb barrier, facilitating a broad programme of nuclear structure and nuclear astrophysics studies using different classes of nuclear reactions.

HIE-ISOLDE REX

The High Intensity and Energy ISOLDE project consists of an upgrade of the ISOLDE facility. The energy of the post-accelerated radioactive beams will be increased from 3 MeV/u to 10 MeV/u. At the same time the intensity of the source will be increased with higher beam power on the production target, from 2 kW to 10 kW.

LINAC

The HIE-REX linac is composed of 6 cryomodules each one containing 5-6 superconducting cavities and 1-2 solenoids. In order to preserve the beam emittances it is important to guarantee a strong focusing in the two transverse planes as well as
the longitudinal plane all along the beam line. This constraint requires the minimization of the drift space between accelerating cavities reducing thus the longitudinal dimension of the interconnection regions. Moreover, in this confined space steering magnets have also to be fitted in order to correct the trajectory of the particles. In the present design the space between two cryomodules is 370 mm of which 90 mm are available for the beam diagnostic boxes, see Figure 1.

HIGH ENERGY BEAM TRANSFER

The HEBT transport system can manage beams with rigidities of up to 2
Tm and is based on a periodic doublet lattice with a period length of 2.62 m, equal to the period length of a single “high-β” cryomodule, operating at a transverse phase advance of 90 degrees. The choice of period length minimises the disruption to the transfer line when each new cryomodule is added to the accelerator in a staged fashion.
The long drift sections house large-angle dipole magnets to steer the beam to different experimental stations. A single type of quadrupole is used throughout the HEBT, specified with a gradient of 25 T/m over an effective length of 20 cm and an inscribed radius of the pole gap of 25 mm.

PROJECT STAGING

Three clear project stages are identified:

Phase 1: maximum energy of 5.5 MeV/u (A/q = 4.5) using 10 cavities housed in two “high-β” cryomodules. Two experimental HEBT beam lines available, with a third beam line as an option (XT01, XT02 and XT03)

Phase 2: maximum energy of 10 MeV/u (A/q = 4.5) using 20 cavities housed in four “high-β” croymodules. Two experimental HEBT beam lines available, with a third beam line as an option (XT01, XT02 and XT03).

Phase 3: maximum energy of 10 MeV/u (A/q = 4.5) using all 32 cavities housed in six croymodules, including two “low-β” and four “high-β” cryomodules. Three experimental HEBT beam lines available (XT01, XT02 and XT03).